In this study, a 2D two-color pyrometer was developed to measure the cathode surface temperature distribution of a high-power hydrogen magnetoplasmadynamic thruster. The developed measurement system consists of an object lens, a beam splitter, bandpass filters, and two cameras. Wavelengths of 950 and 980 nm were selected to achieve a high signal-to-noise ratio by reducing the effects of plasma radiation. The cathode temperature distribution was measured in a discharge current range of 6–13 kA during approximately 1 ms quasi-steady operation. A spot-like high-temperature region over 3000 K and an overall low temperature were observed at low discharge currents. The overall cathode tip region was heated to approximately 2800 K at high discharge currents. The temperature distribution with high temperature only near the cathode tip was measured during quasi-steady operation, the duration of which is shorter than the duration of thermal conduction. These results show that the discharge current distribution near the cathode is stable during the time scale of sub-milliseconds. We confirmed that this temperature distribution remains constant during a 1 ms duty cycle through cathode temperature measurements at each operation time with a 0.2 ms exposure time. The measurement error was approximately 10% of the calculated temperature; a cross-check was performed utilizing near-infrared spectrum measurements.

The flowfields of a self-field magnetoplasmadynamic (MPD) thruster using hydrogen propellant were numerically simulated with a physical model incorporating the ion-slip effect. Thrust performance was investigated for two anode configurations, namely, straight anode and flared anode at discharge currents between 5 to 8 kA. Simulation results show that thrust efficiency increases with increased discharge current for the straight anode, while for the flared anode, thrust efficiency tends to decrease; this opposite trend is caused by the ion-slip effect. When comparing thrust characteristics, thrust for the flared anode was found to be larger than that for the straight anode, but the advantage of the flared anode diminishes at higher discharge currents due to strong pinching and consequent pressure depletion in the vicinity of the flared anode surface. This pressure depletion leads to large electric power consumption owing to the ion-slip heating. That is, at lower pressures, the ion-slip effect becomes more significant because collisions between ions and neutral atoms are not frequent.

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